Since there was recently such a constructive thread on why girls treat guys the way that they do, perhaps there's hope that girls on this message board might be able gain some male insight into why guys treat girls the way that they do.
Here's a case study for you brave souls to analyze (uh, purely hypothetical, of course). Runner guy and runner girl, mid-to-late twenties, date exclusively for over three years. Ups and downs, with a couple of short-term break-ups (once for a week, once for a month, both initiated by girl, who was felt like guy was taking her for granted), but they really hit their stride in the last five months of the relationship. Previous problems had been totally worked through (guy and girl both agreed about that), and even though both were in a time crunch with work, they were creative about finding ways to spend time together despite their busy schedules (which included marathon and triathlon training, separately). While girl was cautious about long-term prospects with guy for the first couple of years, girl finally start to think that things could work out.
Out of the blue, guy says that he doesn't feel right about the relationship, feels like it's stagnant, not "progressing," and he's having trouble seeing it work for the long term. Girl is wondering if they are even talking about the same relationship, but manages to convince him that there's no need to think about the long term for the moment, and guy puts his uneasiness on hold for another couple of weeks to think things over. Finally, though, he can't take it, and breaks up with her, though he says that he still loves her, and still wants to spend time with her post-breakup (only without benefits, of course).
What is going on in this guy's mind (and/or heart)? He clearly thinks that he's doing the right thing by breaking up with her, but does he actually know what he wants? What sort of feeling does he expect to have in order to feel okay about continuing to date this girl? Does he want to feel totally intoxicated and in love every minute that he's with her? Is that the standard for long-term commitment?